1. Field of the Invention
The present invention generally relates to a planar inductor and a method for manufacturing the same, and, in particular, to a planar magnetic inductor, which can realize excellent high frequency characteristics and enhanced inductance with a reduced scale, and a method for manufacturing the same.
2. Description of the Related Art
Inductors have been used for various applications, such as low noise amplifiers, mixers, voltage control oscillators, matching coils, and the like. In particular, a planar inductor is an inductor realized by a conductive coil of a thin film formed on a substrate. Such a planar inductor can be applied to, for example, a DC-DC converter or a noise filter.
Recently, technology has been developed for formation of a magnetic substance together with a conductive coil of a thin film on a substrate in order to enhance performance of the planar inductor. The performance of the planar magnetic inductor is significantly dependent on the properties of the magnetic substance, such as soft magnetic ferrite used for the inductor. The magnetic substance must have a sufficiently high permeability in a high frequency region upon application of high frequency, be prevented from being thermally and mechanically deteriorated during a process of manufacturing the inductor, and be insulated from the conductive coil. Korean Patent Laid-open Publication No. 2003-0020603 discloses technology for manufacturing a thin film inductor in which a dielectric layer is formed between a copper coil and a soft magnetic layer.
FIG. 1 is a schematic cross-sectional view illustrating the construction of a conventional planar magnetic inductor 100. Referring to FIG. 1, the conventional planar magnetic inductor 100 comprises a lower soft magnetic layer 12, a lower dielectric layer 14, a coil-shaped seed layer pattern 16a, and a conductive coil 18 sequentially formed on a substrate 11. An upper soft magnetic layer 24 is formed on the conductive coil 18. These soft magnetic layers 12 and 24 are formed of a Fe or Co-based soft magnetic thin film, and thus have a low specific resistance. Accordingly, in order to prevent electrical short circuit between adjacent lines of the conductive coil 18, a non-magnetic dielectric layer 22 of epoxy or SiO2 is formed, as shown in FIG. 1, in a gap between the lines of the conductive coil 18, and a non-magnetic dielectric layer 14 is also formed under the conductive coil 18. As a result, the overall thickness of the inductor 100 is relatively thickened due to the dielectric layers 14 and 22.
FIGS. 2a to 2d are cross-sectional views illustrating a method for manufacturing the conventional planar magnetic inductor. First, as shown in FIG. 2a, a Fe or Co-based lower soft magnetic layer 12, and a lower dielectric layer 14 are deposited on an insulating substrate 11. Then, as shown in FIG. 2b, a plating seed layer 16 comprising Ni or the like is formed on the lower dielectric layer 14. Then, as shown in FIG. 2c, a conductive coil 18 is formed, and a seed layer pattern 16a is formed to have the same pattern as that of the conductive coil 18 by selectively etching the plating seed layer 16. Next, as shown in FIG. 2d, after an upper dielectric layer 22 is thickly formed, and is flattened such that the conductive coil 18 is completely embedded therein, a Fe or Co-based upper soft magnetic layer 24 is formed thereon. As a result, the sandwich-type planar magnetic inductor 100 is completed.
In the conventional process described above, since the Fe or Co-based upper soft magnetic layers 12 and 24 have a lower specific resistance, the insulating layer 22 formed of oxide or nitride is formed in order to prevent electrical short circuit between the lines of the conductive coil 18. As such, when the insulating layer 22 is formed between the lines of the conductive coil 18, the substrate is exposed to heat generated upon forming the insulating layer 22, causing the magnetic properties of the lower soft magnetic layer 12 to be deteriorated. As a result, bonding strength between the insulating layer 22 and the conductive coil 18 is lowered, thereby causing delamination. Furthermore, since the insulating layer 22 is formed to have a predetermined thickness or more for sufficient electrical insulation, the conductive coil 18 is separated a significant distance from the soft magnetic layers 12 and 24, thereby reducing the inductance and deteriorating high frequency characteristics. Additionally, the overall thickness of the inductor element is increased due to the insulating layers 14 and 22.